Now that we know why we might want to use data persistence, let's get started with some basic knowledge!
Data Persistence literally just means that data is persistent. In other words, it means that data remains even after the program finishes running.
Normally, when programming, we'll store information in variables. Variables are cool and all, but they have one tragic flaw: once a program ends, they lose all of their information.
This means that once a program is done running, all of things we stored in variables will be gone forever (*cue scary sound effect*).
Let's look at an example of this:
def print_some_data():
some_data = input("Enter some data here: ")
print(some_data)This code takes information from the user and then prints it out. But once the program ends, the program forgets everything that it once held. This is why if you run the code several times with different inputs, the result will be different.
But what if the user already wrote some information in another file and we want to print the contents of that file instead of making them re-type everything all over again? Let's take a look at how we can do that:
def printfile(filename):
myfile = open(filename, "r") # open the file
# Now print the lines of the file
for line in myfile:
print(line)
myfile.close()The function printfile will take a string as a parameter. This string is the name of some real file stored in the same folder as the code. Once the function reads the filename, it will open it and read all the lines from the file into a list called lines. In the following for loop, we simply print out each line from that list and call it a day.
Congrats, you've just started your journey into the wonderful world of data persistence! 🚀🛰
Now go and check out using-files.md to get a bit more in-depth!
For more information on this stuff, there are plenty of web pages that talk about file I/O with python. Here's a pretty good one, it is a source for some of the material in this very file! The python documentation is also very helpful, don't be afraid to check it out.